1. Field of the Invention
The present invention relates to a Wideband Code Division Multiple Access (hereinafter referred to as “WCDMA”) telecommunication system. More particularly, the present invention relates to a method for configuring gain factors while reducing signaling overhead in an Enhanced Uplink Dedicated Channel (hereinafter referred to as “E-DCH” or “EUDCH”) for an uplink service.
2. Description of the Related Art
A Universal Mobile Telecommunication Service (hereinafter referred to as “UMTS”) system, which is a 3rd generation mobile telecommunication system based upon European mobile communication systems (i.e., Global System for Mobile Communications (GSM) and General Packet Radio Services (GPRS)) and employing a WCDMA scheme, provides uniform services which enable cellular phone users or computer users to transmit packet-based text, digitized voice, video or multimedia data at a higher speed than 2 Mbps no matter where they are located.
The UMTS system uses an E-DCH in order to further improve performance of packet transmission in a reverse communication, that is, an uplink (UL) communication from a User Terminal or User equipment (hereinafter referred to as “UE”) to a Node B. In order to provide more stable high-speed data transmission, the E-DCH supports various techniques such as Adaptive Modulation and Coding (hereinafter referred to as “AMC”), Hybrid Automatic Retransmission Request (hereinafter referred to as ‘HARQ’), Node-B controlled scheduling, shorter Transmission Time Interval (hereinafter referred to as “TTI”) length and so forth.
The AMC is a technique for improving resource use efficiency by determining a modulation scheme and a coding scheme for a data channel according to channel conditions between a Node B and a UE. A combination of the modulation scheme and the coding scheme is called a Modulation and Coding Scheme (hereinafter referred to as “MCS”), and many MCS levels may be defined according to supportable modulation schemes and coding schemes. The AMC determines the MCS level according to channel conditions between a Node B and a UE, thereby improving the resource use efficiency.
The HARQ refers to a technique in which, when errors occur in an initially transmitted data packet, the packet is retransmitted in order to compensate for the erroneous packet. This HARQ may be classified into a Chase Combining (hereinafter referred to as “CC”) technique and an Incremental Redundancy (hereinafter referred to as “IR”) technique. In the CC technique, packets having the same format as that at initial transmission are retransmitted when errors occur. In the IR technique, packets having the different format than that at initial transmission are retransmitted when errors occur.
The Node B-controlled scheduling is a scheme in which a Node B determines whether to transmit uplink data on an upper limit value of possible data rates and transmits the determined information as scheduling allocation information to a UE when data is transmitted using an E-DCH. In turn, the UE determines a possible data rate of an uplink E-DCH with reference to the scheduling allocation information.
The shorter TTI length permits a TTI shorter than 10 ms corresponding to a minimum TTI of a typical Dedicated Channel (DCH), thereby reducing retransmission time and thus enabling high system throughput.
FIG. 1 is a view for explaining uplink packet transmission over an E-DCH in a typical radio telecommunication system. In the drawing, reference numeral “100” designates a base station supporting an E-DCH service, that is, a Node B, and reference numerals “101”, “102”, “103” and “104” designate UEs using the E-DCH service. As shown in FIG. 1, the UEs 101, 102, 103, 104 transmit data to the Node B 100 over E-DCHs 111, 112, 113, 114, respectively.
Using data buffer statuses, requested data rates or channel condition information of the UEs 101 to 104, the Node B 100 informs each UE 101 to 104 of whether or not E-DCH data transmission is possible for the corresponding UE or performs a scheduling operation for coordinating E-DCH data rates. The scheduling is performed in such a manner that lower data rates are assigned to UEs far away from the Node B 100 (for example, the UEs 103, 104) and higher data rates are assigned to UEs near to the Node B (for example, the UEs 101, 102), while a measured Noise Rise or Rise over Thermal (hereinafter referred to as “RoT”) value of the Node B does not exceed a target value in order to enhance the overall system performance.
FIG. 2 is a message flowchart illustrating typical transmission/reception procedures over an E-DCH.
Referring to FIG. 2, in step 202, an E-DCH is set up between a Node B and a UE. This E-DCH setup is implemented through processes of transmitting/receiving messages over a dedicated transport channel. In step 204, the UE informs the Node B of scheduling information comprising transmission power information of the UE, which represents uplink channel conditions, information on transmission power margin which the UE can transmit, the amount of data, which are stacked up in a buffer of the UE and awaiting transmission, and so on.
In step 206, the Node B monitors scheduling information of a plurality of UEs including the above-mentioned UE in order to schedule data transmissions of the plurality of UEs. In step 208, using the scheduling information received from the UE, the Node B determines to grant packet transmission to the UE and transmits scheduling assignment information to the UE. The scheduling assignment information comprises a granted data rate and granted transmission timing.
In step 210, using the scheduling assignment information, the UE determines a Transport Format (hereinafter referred to as “TF”) signifying a transmission rate and transmission power of the E-DCH. The UE transmits uplink packet data over the E-DCH according to the TF in step 214, and preferably simultaneously transmits the TF information to the Node B in step 212. Here, the TF information comprises a Transport Format resource Indicator (hereinafter referred to as “TFRI”) representing information on resources necessary for receiving the E-DCH. In step 214, the UE also selects a MCS level in consideration of the data rate assigned by the Node B and channel conditions, and transmits the uplink packet data by using the MCS level.
In step 216, the Node B determines if errors occur in the TF information and the packet data. In step 218, the Node B transmits NACK (Negative Acknowledge) over an ACK/NACK channel when the determination proves both or either of the TF information and the packet data to be erroneous, or transmits ACK (Acknowledge) over the ACK/NACK channel when the determination proves both of the TF information and the packet data to have no errors. The packet data transmission is completed and the UE transmits new user data over the E-DCH when the Node B transmits the ACK, but the UE retransmits packet data having the same contents as those of the previously transmitted packet data over the E-DCH when the Node B transmits the NACK.
In the environment described above, the Node B improves the overall system performance by assigning lower data rates to UEs far away from the Node B that have worse channel conditions or are to be provided with a low priority data service, and assigning higher data rates to UEs near to the Node B that have better channel condition or are to be provided with a high priority data service.
TFs of an E-DCH, to which the Node B-controlled scheduling technique, the HARQ technique and the like are applied, are diversely configured according to service types and data rates. The respective TFs define the overall size of an E-DCH Transport Block (hereinafter referred to as “TB”) by the size and number data blocks, and thus represent individual data rates different from each other. TF sets available for the E-DCH are configured such that they have various data rates in order to efficiently transmit a Protocol Data Unit (hereinafter referred to as “PDU”) transferred from an upper layer with as little padding as possible. For example, the total number of TF sets for the E-DCH is about 128 to 256.
FIG. 3 illustrates an example of typical TF configuration. As shown in the drawing, TF Index (hereinafter referred to as “TFI”) 0 to TFI 11 identifying TFs indicate TB size Ninfo in a range of 128 to 8192 bits, respectively.
In order to transmit a transport channel for the E-DCH, a Dedicated Physical Data Channel for E-DCH (hereinafter referred to as “E-DPDCH”) has been introduced in a physical layer. Power required to stably transfer data over the E-DPDCH is determined by configuring a gain factor representing a power ratio of the E-DPDCH to a Dedicated Physical Control Channel (hereinafter referred to as “DPCCH”), which is used as a pilot channel.
The gain factor has different values from TF to TF because the amount of overall power requirement is different according to transmission rates. In other words, since data reception performance is determined by transmission bit energy, that is, Eb, packet transmission quality of the system is maintained only by keeping the transmission bit energy constant. In order to keep the transmission bit energy constant, the amount of overall power requirement differs from transmission rate to transmission rate.
Hereinafter, a description will be given of a method for configuring gain factors for an uplink Dedicated Physical Data Channel (hereinafter referred to as “DPDCH”), to which an uplink Dedicated Channel (hereinafter referred to as “DCH”) is mapped, on a TF-by-TF basis.
A network represented by a Radio Network Controller (hereinafter referred to as “RNC”) configures transmission power, which is necessary for each TF to maintain constant quality, by using gain factors. A gain factor configuration method is classified into a signaled gain factor scheme and a computed gain factor scheme. In the signaled gain factor scheme, the network informs a UE of TF-by-TF gain factors through upper layer signaling. In the computed gain factor scheme, the network informs a UE only of gain factors for a reference TF Combination (hereinafter referred to as “TFC”) representing a combination of reference TFs and transport channels, and the UE personally calculates and determines gain factors for the other TFs based on the gain factors for the reference TFC.
The conventional computed gain factor scheme is expressed by the following Equation (1). As described below, a ratio of a gain factor for a specific TFC to a gain factor for a reference TFC is given as a ratio of a transmission rate for a desired TFC and a transmission rate for the reference TFC:
                              A          j                =                                                            β                                  d                  ,                  ref                                                            β                                  c                  ,                  ref                                                      ·                                                            L                  ref                                                  L                  j                                                              ⁢                                                    K                j                                            K                ref                                                                        (        1        )            where, Aj denotes a power ratio of a DPDCH to a DPCCH for a desired j-th TF. βd,ref and βc,ref denote a DPDCH gain factor and a DPCCH gain factor for a reference TF, respectively, Lref denotes the number of DPDCHs necessary for supporting a reference TFC, and Lj denotes the number of DPDCHs necessary for transmitting a desired j-th TFC. Kref and Kj denote transport channel data sizes for the reference TFC and the j-th TFC, respectively, which are obtained as follows:
                                          K            ref                    =                                    ∑              i                                                                    ⁢                                                  ⁢                                          RM                i                            ·                              N                                  i                  ,                  ref                                                                    ⁢                                  ⁢                              K                          j              ⁢                                                                            =                                    ∑              i                                                                    ⁢                                                  ⁢                                          RM                i                            ·                              N                                  i                  ,                  j                                                                                        (        2        )            
The transport channel data size is the sum of data bits of all transport channels mapped to a corresponding physical channel. The data bits of the respective transport channels are not multiplexed together, but pass through coding and rate matching according to weights of the respective transport channels and then are summated. A fraction of bits punched or repeated by the rate matching is determined by a rate matching attribute value RM disclosed through upper layer signaling. In Equation (2), RMi denotes a rate matching attribute value of an i-th transport channel, and Ni,ref and Ni,j denote data sizes after coding but before rate matching for the i-th transport channel. Therefore, Kref and Kj become transport channel data size multiplexed after rate matching in a case of using the corresponding TFC.
Since a plurality of transport channels are mapped to one DPDCH, and these transport channels have different coding rates and rate matching ratios, the gain factors are calculated using data sizes to which rate matching attribute values RM are applied as stated above.
Once a value of Aj representing the power ratio of the DPDCH to the DPDCCH is obtained in Equation (1), each gain factor can be derived from the value of Aj. That is, a gain factor for the j-th TFC is as follows:If Aj>1, then βd,j=1.0 and βc,j=1/Aj,If Aj<=1, then βc,j=1.0 and βd,j=1/Aj  (3)
Both of the conventional gain factor configuration schemes require Radio Resource Control (hereinafter referred to as “RRC”) signaling between the UE and the RNC. In the signaled gain factor scheme, since all TFs needed TF by TF are provided to the UE, significant signaling resources are consumed. Also, in the computed gain factor, the RNC must notify the UE of gain factors for the reference TFCs and information on the relationships between the respective TFCs and the reference TFCs through RRC signaling. Accordingly, the computed gain factor scheme also consumes significant signaling resources.
FIG. 4 illustrates information elements (hereinafter referred to as “IE”) of a signaling message for the conventional gain factor configuration. As shown in the drawing, IE “CHOICE Gain Factors” for gain factor choice comprises IE “Signaled Gain Factors” and IE “Computed Gain Factors”. In order to perform signaling of gain factors for reference TFCs, the IE “Signaled Gain Factors” comprises FDD and TDD fields representing whether a choice mode is a Frequency Division Duplex (FDD) mode or a Time Division Duplex (TDD) mode. When the choice mode is the FDD, a DPDCCH gain factor βc, DPDCH gain factors βd for the respective reference TFCs, and reference TFC IDs for the respective TFCs are also included in the IE “Signaled Gain Factors”. In addition, to apply the computed gain factor scheme to non-signaled TFCs, reference TFC IDs corresponding to the respective TFCs are included in the IE “Computed Gain Factors”.
Accordingly, a need exists for a method for configuring gain factors in a WCDMA telecommunication system in which the gain factor for defining power required for normal reception of uplink data in an environment supporting an uplink service over an E-DCH can be configured using minimal signaling information.